1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __LINUX_INSTRUMENTATION_H
3 #define __LINUX_INSTRUMENTATION_H
4
5 #ifdef CONFIG_NOINSTR_VALIDATION
6
7 #include <linux/stringify.h>
8
9 /* Begin/end of an instrumentation safe region */
10 #define __instrumentation_begin(c) ({ \
11 asm volatile(__stringify(c) ": nop\n\t" \
12 ".pushsection .discard.instr_begin\n\t" \
13 ".long " __stringify(c) "b - .\n\t" \
14 ".popsection\n\t" : : "i" (c)); \
15 })
16 #define instrumentation_begin() __instrumentation_begin(__COUNTER__)
17
18 /*
19 * Because instrumentation_{begin,end}() can nest, objtool validation considers
20 * _begin() a +1 and _end() a -1 and computes a sum over the instructions.
21 * When the value is greater than 0, we consider instrumentation allowed.
22 *
23 * There is a problem with code like:
24 *
25 * noinstr void foo()
26 * {
27 * instrumentation_begin();
28 * ...
29 * if (cond) {
30 * instrumentation_begin();
31 * ...
32 * instrumentation_end();
33 * }
34 * bar();
35 * instrumentation_end();
36 * }
37 *
38 * If instrumentation_end() would be an empty label, like all the other
39 * annotations, the inner _end(), which is at the end of a conditional block,
40 * would land on the instruction after the block.
41 *
42 * If we then consider the sum of the !cond path, we'll see that the call to
43 * bar() is with a 0-value, even though, we meant it to happen with a positive
44 * value.
45 *
46 * To avoid this, have _end() be a NOP instruction, this ensures it will be
47 * part of the condition block and does not escape.
48 */
49 #define __instrumentation_end(c) ({ \
50 asm volatile(__stringify(c) ": nop\n\t" \
51 ".pushsection .discard.instr_end\n\t" \
52 ".long " __stringify(c) "b - .\n\t" \
53 ".popsection\n\t" : : "i" (c)); \
54 })
55 #define instrumentation_end() __instrumentation_end(__COUNTER__)
56 #else /* !CONFIG_NOINSTR_VALIDATION */
57 # define instrumentation_begin() do { } while(0)
58 # define instrumentation_end() do { } while(0)
59 #endif /* CONFIG_NOINSTR_VALIDATION */
60
61 #endif /* __LINUX_INSTRUMENTATION_H */
62
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